Abrasion-resistant implantable medical lead and a method of fabricating such a lead

ABSTRACT

An implantable medical lead comprises an insulating lead body housing having an outer surface. A thin, flexible membrane surrounds the insulating housing, the membrane having an inner surface confronting the outer surface of the housing. A lubricious interface between the inner surface of the membrane and the outer surface of the housing facilitates movement of the insulating housing relative to the membrane in response to frictional engagement of the membrane with adjacent structure. Also disclosed is a method of fabricating such a lead.

FIELD OF THE INVENTION

The present invention relates generally to implantable medical leads foruse with implantable medical devices such as pacemakers and/orcardioverter/defibrillators, and more particularly to an implantablemedical lead comprising a composite lead body having a lubriciousinterface that imparts abrasion resistance to the lead body.

BACKGROUND OF THE INVENTION

Various kinds of implantable medical leads for providing stimulation toselected body tissue have become available. For example, an implantablecardiac lead delivers electrical therapy to a patient's heart throughone or more electrodes on the distal end of the lead. The electrodes areconnected via electrical conductors to a connector assembly on theproximal end of the lead. The connector assembly is in turn coupled toan implantable medical device (IMD) such as a pacemaker or animplantable cardioverter-defibrillator (ICD) or to an IMD combining bothpacemaker and ICD functions.

The electrical conductors of an implantable lead are enclosed within anelongated, typically tubular housing made of an insulating material suchas silicone rubber or polyurethane. Silicone rubber is known to havesuperior flexibility and long term biostability but has relatively poorabrasion and tear resistance. Polyurethane, on the other hand, is moreresistant to abrasion, cuts and tears but is susceptible tobiodegradation and is somewhat stiffer than silicone rubber.

It is desirable that the outer surface of an implantable medical leadhave resistance to abrasive wear in the event the lead body rubs againstanother lead, another implanted device, or the patient's anatomicalstructure while in use after implantation. Abrasive wear can eventuallycause breaks or tears in the lead body's insulating housing andconsequent failure of the electrical connection provided by one or moreof the electrical conductors. A short circuit, in particular, canpotentially damage the circuits of the IMD to an extent requiring itsreplacement. Insulation abrasion failures account for the largestproportion of all failures in silicone rubber insulated leads.

Thus, there continues to be a need for implantable medical leads, andparticularly those with silicone rubber housings, having improvedabrasion and tear resistant properties.

SUMMARY

In accordance with one specific, exemplary embodiment of the presentinvention, there is provided an implantable medical lead comprising alead body having a proximal end carrying a connector assembly adapted tobe received by an implantable medical device, and a distal end carryingat least one electrode. The lead further includes an insulating housinghaving an outer surface and enclosing at least one electrical conductorconnecting the at least one electrode with a terminal contact on theconnector assembly. A thin, flexible membrane surrounds the insulatinghousing, the membrane having an inner surface confronting the outersurface of said housing. A lubricious interface between the innersurface of said membrane and the outer surface of the housingfacilitates movement of the insulating housing relative to the membranein response to frictional engagement of the membrane with adjacentstructure. The flexibility of the membrane and the properties of thelubricious interface are such that the membrane will slide over the leadbody housing and stretch, wrinkle, twist or wind as the lead bodyhousing moves relative to the patient's body tissue such as the wall ofa vein. The relative motion between the membrane and the housing greatlyreduces abrasive wear of the lead body. Further, the invention preservesthe small outer diameter of the lead, as well as lead flexibility andisodiametric features.

In accordance with another aspect of the invention, the confrontingsurfaces of the membrane and the housing define between them a sealedspace containing the lubricious interface. Further in this regard, themembrane may have a sealed distal end located proximally of the at leastone electrode and a sealed proximal end located distally of theconnector assembly.

In accordance with one preferred form thereof, the lubricious interfacemay comprise a biostable, biocompatible, medical grade material selectedfrom the group consisting of silicone oil, silicone gel, silicone foam,silicone grease, PTFE powder, mineral oil, mineral paste and mineralpowder. In accordance with another preferred form thereof, thelubricious interface may comprise a lubricious coating on the innersurface of the membrane, on the outer surface of the housing, or on bothsurfaces.

Pursuant to another aspect of the invention, the membrane may bedisposed over the outer surface of the housing in an interference fit, aclearance fit, or an even fit. Preferably, the insulating housing may befabricated of silicone rubber, while the membrane may comprise abiostable, biocompatible, medical grade, elastic material selected fromthe group consisting of silicone rubber, polyurethane, polyester, awoven fabric, a knitted fabric, a composite fabric, a memory shapedpolymer and a silicone-urethane copolymer.

In accordance with still another specific, exemplary embodiment of theinvention, the distal end of the lead body may carry at least twospaced-apart electrodes comprising a distal electrode and a proximalelectrode, the mentioned membrane being located between the distal andthe proximal electrodes. In this embodiment, the lead further includes asecond, thin, flexible membrane surrounding the insulating housing, thesecond membrane being located between the proximal end of the proximalelectrode and the distal end of the connector assembly. The secondmembrane has an inner surface confronting the outer surface of saidhousing, and a lubricious interface, preferably in one of the formsdescribed above, between the inner surface of the second membrane andthe outer surface of the housing facilitates movement of the insulatinghousing relative to the second membrane in response to frictionalengagement of the second membrane with adjacent structure.

In accordance with another specific, exemplary aspect of the presentinvention, there is provided a method of fabricating anabrasion-resistant implantable medical lead comprising a distal endcarrying at least one electrode electrically connected to a contact on aconnector assembly attached to a proximal end of the lead, and aninsulating housing having an outer surface. The method comprises thesteps of enclosing a portion of the housing in a membrane having adistal end and a proximal end, sealing one of the ends of the membraneto the outer surface of the housing adjacent the at least electrode oradjacent the connector assembly, injecting a lubricious medium into thespace defined between the membrane and the outer surface of the housing,and sealing the other end of the membrane to the outer surface of thehousing. Preferably, the membrane comprises a thin, stretchable, tubularstructure, and before the second sealing step, the membrane is stretchedso that it lies against the outer surface of the housing, the housingand the membrane being dimensioned for an interference fit.Alternatively, the housing and the membrane may be dimensioned for aclearance fit, or for an even fit.

An alternative embodiment of the method of the present invention forfabricating an abrasion-resistant implantable medical lead comprises thesteps of enclosing a portion of the lead body housing in a membranehaving a distal end and a proximal end, sealing the ends of the membraneto the outer surface of the housing, and injecting a lubricious mediumthrough the membrane into the space defined between the membrane and theouter surface of the housing. If necessary, the portion of the membranethrough which the lubricious medium was injected is sealed with, forexample, a medical adhesive.

Yet another alternative embodiment of the method of the presentinvention for fabricating an abrasion-resistant implantable medical leadcomprises the steps of providing an insulating housing having an outersurface, enclosing a portion of the housing in a membrane having aninner surface, a distal end and a proximal end, the outer surface of thehousing or the inner surface of the membrane or both of those surfaceshaving a lubricious coating, and attaching the ends of the membrane tothe outer surface of the housing.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, features and advantages of theinvention will be evident to those skilled in the art from the detaileddescription below, taken together with the accompanying drawings, inwhich:

FIG. 1 is a side view of an implantable cardiac pacing, sensing andcardioverting/defibrillating system, including a lead in accordance withone embodiment of the present invention;

FIG. 2 is a transverse cross section view of the lead shown in FIG. 1 asseen along the line 2—2 in FIG. 1;

FIG. 3 is an axial cross section view of a portion of the lead shown inFIG. 1 as seen along the line 3—3 in FIG. 2;

FIG. 4 is a side view of an implantable cardiac pacing, sensing andcardioverting/defibrillating system, including a lead in accordance withan alternative embodiment of the invention; and

FIG. 5 is an axial cross section view of a portion of a lead inaccordance with yet another alternative embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The following description is of a best mode presently contemplated forpracticing the invention. This description is not to be taken in alimiting sense but is made merely for the purpose of describing thegeneral principles of the invention whose scope is defined by theappended claims. Although the invention will be described in the contextof implantable cardiac stimulation and sensing leads, it will be evidentto those skilled in the art that the invention described herein hasbroader utility, being applicable to a wide variety of implantablemedical leads for stimulating selected body tissue and sensing theelectrical activity of such tissue.

By way of example and not limitation, FIGS. 1–3 show an endocardialpacing, sensing and defibrillation system 10 comprising a lead 12 and animplantable medical device (IMD) 14 that may comprise a pacemaker/ICD.The lead 12 includes a lead body 16 having a proximal end 18 and adistal end 20. The lead 12 is illustrated to be of a quadripolar design,but is not intended to be limiting of the invention. The proximal end 18of the lead 12 incorporates a connector assembly 22 compatible with astandard such as the IS-4 standard for connecting the lead body to theIMD 14. The connector assembly 22 includes a tubular pin terminalcontact 24 and ring terminal contacts 26–28 electrically coupled toelectrodes along the distal end 20 of the lead body. The connectorassembly 22 of the lead is received within a receptacle (not shown) inthe IMD 14 containing electrical terminals positioned to engage thecontacts 24 and 26–28 on the connector assembly 22. As is well known inthe art, to prevent ingress of body fluids into the receptacle, theconnector assembly 22 is provided with spaced sets of seals 30. Inaccordance with standard implantation techniques, a stylet or guide wire(not shown) for delivering and steering the distal end of the lead bodyduring implantation is inserted into a lumen of the lead body throughthe tubular connector terminal pin 24.

The lead body 16 extends along a central, longitudinal axis 32 andpreferably comprises a tubular sheath or housing 34 made of aninsulating, biocompatible, biostable polymer, for example, siliconerubber or polyurethane. Although various insulating housing materialsare intended to be encompassed by the invention, silicone rubber isoften preferred because of its flexibility and long term biostability.

The distal end 20 of the lead body may carry one or more electrodeswhose configurations, functions and placement along the length of thedistal end will be dictated by the indicated stimulation therapy, thepeculiarities of the patient's anatomy, and so forth. The lead body 16illustrates but one example of the various combinations of stimulatingand/or sensing electrodes that may be utilized. More particularly, thedistal end 20 of the lead body terminates at a distal extremity 36incorporating an electrical stimulating and/or sensing tip electrode 38.As is well known in the art, the distal end of the lead body is placedso as to position the surface of the tip electrode 38 in electricalcommunication with the body tissue to be stimulated and/or sensed.

In conventional fashion, the distal end 20 of the lead body may includepassive fixation means (not shown) that may take the form ofconventional projecting tines for anchoring the lead body within theright atrium or right ventricle of the heart. Alternatively, the passivefixation or anchoring means may comprise one or more preformed humps,spirals, S-shaped bends, or other configurations manufactured into thedistal end 20 of the lead body 16 where the lead is intended for leftheart placement within a vessel of the coronary sinus region. Thefixation means may also comprise an active fixation mechanism such as ahelix. It will be evident to those skilled in the art that anycombination of the foregoing fixation or anchoring means may beemployed.

The distal end 20 of the lead body may also carry one or more ringelectrodes as well as one or more cardioverting/defibrillating coils. Inthe example under consideration, two ring electrodes 40 and 42 and asingle cardioverting/defibrillating coil 44 are included. The ringelectrodes 40 and 42 may serve as both tissue-stimulating and sensingelectrodes. Other electrode configurations may, of course, be employedpursuant to lead constructions well known in the art. For example, analternative electrode arrangement may include additional ringstimulation and/or sensing electrodes as well as additionalcardioverting and/or defibrillating coils spaced apart along the distalend of the lead body. Thus, as emphasized, FIGS. 1–3 are illustrativeonly; the distal end of the lead body may carry only pacing and sensingelectrodes, only cardioverting/defibrillating electrodes or acombination of pacing, sensing and cardioverting/defibrillatingelectrodes. Where defibrillating electrodes are included these may be ofconventional coil design or, for greater flexibility, they may comprisespaced apart, relatively short metallic rings or they may be made of anelectrically conductive polymer or coating. The kind of electrodeconfiguration used will depend upon the particular application andaccordingly any electrode configuration known in the art or developed inthe future may be utilized. The ring and cardioverting/defibrillatingelectrodes 40, 42 and 44 shown in the example are electrically connectedto the ring terminal contacts 26–28 on the connector assembly 22.

In accordance with one form of the invention, the lead body 16 may beisodiametric, that is, the outside diameter of the lead body may be thesame throughout its entire length. By way of example and not limitation,the outside diameter of the lead body 16 may range from about 0.026 inch(2F) to about 0.130 inch (10F). Also, in accordance with well knowntechniques, the outer surface of the lead body 16 may have a lubriciouscoating along its length to facilitate its movement through a leaddelivery introducer and the patient's vascular system.

The insulating housing 34 may have various cross-sectionalconfigurations. In the example shown, the housing 34 comprises atubular, multilumen structure having an outer, generally cylindricalsurface 50 (FIGS. 2 and 3). More specifically, the lead body housing 34is a quadrilumen structure defining four axially or longitudinallyextending, parallel passages or lumens comprising a central lumen 52 andthree outer lumens 54–56 disposed about the central lumen 52. Thecentral lumen 52 may enclose a low friction liner of PTFE, for example(not shown), through which a stylet, guide wire, or inner coil may bepassed for delivering and steering the distal of the lead body duringimplantation thereof. In the example shown, the central lumen 52contains an electrical coil conductor 58 connecting the tip electrode 38to the pin terminal contact 24 on the connector assembly 22.

The lumens 54–56 contain insulated electrical conductors 60–62,respectively, that may each be in the form of a multifilar, braidedcable typically of MP35N or MP35N/Ag alloy. Alternatively, one or moreof the conductors 60–62 may comprise monofilament, non-coiled wires of,for example, nitinol, MP35N, or the like. The cable or wire conductors60–62 connect the various ring and cardioverting/defibrillatingelectrodes 40, 42 and 44 on the distal end of the lead body with theassociated terminal contacts 26–28 on the proximal connector assembly.

In accordance with one specific, exemplary embodiment of the invention,the lead body housing 34 between the connector assembly 22 and theproximal end of the cardioverting/defibrillating electrode 44 isenclosed within a thin, flexible, stretchable, sleeve-like or tubular,polymer membrane 66. The tubular membrane 66 has a distal end 68adjacent to the proximal end of the cardioverting/defibrillatingelectrode 44, a proximal end 70 adjacent to the distal end of theconnector assembly 22, and an inner surface 72 confronting the outersurface 50 of the housing 34. The distal end 68 of the tubular membraneis attached to the outer surface 50 of the housing by means of acontinuous, fluid-tight, circumferential seal 74 of medical adhesive ora comparable bonding agent. A similar circumferential seal 76 of medicaladhesive or comparable bond attaches the proximal end 70 of the membraneto the outer surface of the housing. The confronting inner surface 72 ofthe membrane and the outer surface 50 of the housing thus define a thin,annular, fluid-tight interface space 78 sealed at its opposite ends. Inthe embodiment of FIGS. 1–3, the space 78 contains a lubriciousinterface in the form of a lubricious medium 80.

Without limitation, the following material and dimensional examples areprovided:

A. The membrane 66 may be made of any thin, flexible (that is,stretchable), biocompatible, biostable material such as, withoutlimitation, any of the following:

-   -   1. Medical grade elastomeric silicone rubber;    -   2. Medical grade elastic polyurethane;    -   3. Medical grade elastic polyester;    -   4. Woven, knitted, or composite fabrics with controlled stretch;    -   5. Flexible plastic memory shaped polymers; and    -   6. Silicone-urethane copolymers.

B. The thickness of the membrane 66 in its relaxed state may range fromabout 0.0005 inch to about 0.005 inch.

C. The lubricious medium 80 contained within the interface space 78 maycomprise, without limitation:

-   -   1. A medical grade silicone oil, gel, foam or grease;    -   2. A medical grade PTFE powder; or    -   3. A hydrocarbon agent such as mineral oil, paste or powder.

D. By way of example only, the volume of the lubricious medium 80injected into the space 78 may comprise approximately 0.01 cc per linearcentimeter of the length of the space 78.

The tubular membrane 66 is slid into place over the housing preferablyin an interference fit so that the membrane is stretched longitudinallyand circumferentially over the outer surface of the housing 34 when itis installed. For example, the housing may have an outer diameter of0.060 inch while the membrane may have an inner diameter of 0.058 inchin its unstretched state. Using a medical adhesive or comparable bondingagent, one end 68 or 70 of the tubular membrane 66 is then attached tothe outer surface 50 of the housing 34 about the entire circumference ofthe housing to seal the one end of the membrane at 74 or 76. Thelubricious medium 80 is then injected into the interface space 78; themedium will form a thin film within the space 78. The other end 68 or 70of the membrane is then similarly attached to the outer surface 50 ofthe housing to completely seal the filled interface space 78.Alternatively, both ends of the membrane 66 may be sealed followed byinjection of the medium 80 through the wall of the membrane using ahypodermic needle or comparable expedient. If necessary, the puncturethrough the membrane may be sealed with medical adhesive. Alternatively,instead of an interference fit between the housing and the membrane,these elements may be dimensioned for a clearance fit or an even fit. Byway of example, an appropriate interference fit may be obtained when,prior to assembly of the housing 34 and the membrane 66, the diameter ofthe outer surface 50 of the housing 34 is greater, for example, by 0.001inch, than the diameter of the inner surface 72 of the membrane 66 inits unstretched state. A clearance fit may be obtained when prior toassembly the diameter of the housing surface 50 is less, for example, by0.001 inch than the diameter of the membrane surface 72. An even fit maybe obtained when the aforementioned diameters are the same prior toassembly.

Turning now to FIG. 4, there is shown an implantable cardiac pacing,sensing and cardioverting/defibrillating system 100 that includes a lead102 in accordance with an alternative embodiment of the invention.Generally, the description of the lead shown in FIG. 1 is applicable tothe alternative embodiment of FIG. 4. Thus, the lead 102 includes a leadbody 104 having a connector assembly 106 at a proximal end 108 of thelead body. The connector assembly 106 is adapted to be received by anIMD such as a pacemaker/ICD 110. A plurality of spaced-apart electrodes112–115 including a cardioverting/defibrillating electrode 115 aredisposed along a distal end 116 of the lead body. Thecardioverting/defibrillating electrode 115 may be positioned along thedistal end of the lead body so as to provide electrical stimulation to,for example, the right ventricle of the heart. In addition to thecardioverting/defibrillating electrode 115, the embodiment of FIG. 4includes a second cardioverting/defibrillating electrode 118 disposedalong the distal end 116 proximally of the firstcardioverting/defibrillating electrode 115 and positioned to stimulate,by way of example, the tissue of the superior vena cava (SVC). The leadbody 104 includes a polymer, tubular housing 120 of silicone rubber orthe like having an outer surface 122.

In accordance with the alternative embodiment of FIG. 4, the portion ofthe lead body housing 120 between the cardioverting/defibrillatingelectrodes 115 and 118 is enclosed within a first membrane 124 havingthe properties already described in connection with the firstembodiment. The membrane 124 has a distal end 126 adjacent to theproximal end of the first cardioverting/defibrillating electrode 115 anda proximal end 128 adjacent to the distal end of the secondcardioverting/defibrillating electrode 118. The membrane ends 126 and128 are attached to the outer surface 122 of the lead body housing 120by means of continuous, fluid tight, circumferential seals of medicaladhesive or a comparable bonding agent in the manner already described.The portion of the lead body housing 120 between the proximal end of thesecond cardioverting/defibrillating electrode 118 and the distal end ofthe connector assembly 106 is enclosed within a second membrane 130having the properties already described. The membrane 130 is attached tothe outer surface 122 of the lead body housing 120 by means ofcontinuous, fluid tight, circumferential seals at opposed, distal andproximal ends 132 and 134, respectively, of the membrane. As before, theannular, thin, fluid-tight interface spaces between the membranes 124and 130, on the one hand, and the outer surface 122 of the housing 120,on the other, each contains a lubricious interface in the form of alubricious medium, all as previously described.

In accordance with another specific embodiment of the invention, thelubricious interface between the membrane(s) and the associated leadbody housing may comprise, instead of an injectable medium, varioussurface treatments or surface modifications such as lubricious thinfilms or coatings. Thus, with reference to FIG. 5, there is shown inaxial cross-section a portion of a lead body 150 including, as before, alead body housing 152 having an outer surface 154. The outer surface 154of the lead body housing along at least a portion of the length thereofis enclosed within a membrane 156 of the kind previously described. Themembrane 156 has an inner surface 158 confronting the outer surface 154of the lead body housing 152. Disposed between the confronting innersurface 158 of the membrane 156 and the outer surface 154 of the housing152 is a lubricious interface that, in accordance with the specific,exemplary embodiment of FIG. 5, comprises a lubricious film or coating160 on the inner surface 158 of the membrane 156 and a lubricious filmor coating 162 on the outer surface 154 of the lead body housing. Itwill be evident that instead of providing a lubricious film or coatingon each of the two surfaces 154 and 158, such a film or coating may beprovided on only one of the two surfaces. The lubricious film or coating160, 162 may take the form of any of the well known lubricious films orcoatings that are presently applied to the outer surface of implantableleads, for example, the molecular coatings on cardiac leads sold by St.Jude Medical, Inc., under the registered trademark, “FAST-PASS”. It willbe evident that the embodiment of FIG. 5 is applicable to the singlemembrane lead body structure of FIGS. 1–3 as well as to the multiplemembrane structure of FIG. 4.

The flexibility of the membrane(s) and the properties of the lubriciousinterface of the various embodiments disclosed herein are such that themembrane(s) will slide over the lead body housing and stretch, wrinkle,twist or wind as the lead body housing moves relative to the patient'sbody tissue such as the wall of a vein. The relative motion between themembrane(s) and the housing greatly reduces abrasive wear of the leadbody. Further, the invention preserves the small outer diameter of thelead, as well as lead flexibility and isodiametric features. Moreover,it will be apparent that the invention is applicable to all implantablemedical leads, including both endocardial and epicardial cardiac leads.

While several illustrative embodiments of the invention have been shownand described, numerous variations and alternative embodiments willoccur to those skilled in the art. Such variations and alternativeembodiments are contemplated, and can be made without departing from thespirit and scope of the invention as defined in the appended claims.

1. An implantable medical lead comprising: a lead body having a proximalend carrying a connector assembly adapted to be received by animplantable medical device and a distal end, and at least one electrodefor patient stimulation connected to said lead body; said lead bodyfurther comprising: an insulating housing defining an outer surface andenclosing at least one electrical conductor connecting said at least oneelectrode with said connector assembly; a flexible membrane surroundingsaid insulating housing, said membrane inner surface confronting saidouter surface of said insulating housing; a distal circumferential sealattaching a distal portion of said membrane to said outer surface ofsaid insulating housing; a proximal circumferential seal attaching aproximal portion of said membrane to said outer surface of saidinsulating housing; wherein said distal circumferential seal and saidproximal circumferential seal define a sealed space between said innersurface of said membrane and said outer surface of said insulatinghousing; and a lubricious medium disposed within said sealed space;wherein flexibility of the membrane and the properties of the lubriciousmedium enable said membrane to slide over said insulating housing anddeform as said insulating housing moves relative to a patient's bodytissue; and wherein relative motion between said membrane and saidinsulating housing reduces abrasive wear of said lead body.
 2. The leadof claim 1 in which: said distal circumferential seal is locatedproximally of said at least one electrode and said proximalcircumferential seal is located distally of the connector assembly. 3.The lead of claim 1 in which: said lubricious medium comprises abiostable, biocompatible, medical grade material selected from the groupconsisting of silicone oil, silicone gel, silicone foam, siliconegrease, PTFE powder, mineral oil, mineral paste and mineral powder. 4.The lead of claim 1 in which: the volume of said lubricious mediumcontained in said sealed space comprises approximately 0.01 cc perlinear cm of the length of said sealed space.
 5. The lead of claim 1 inwhich: said lubricious medium comprises a lubricious coating on at leastone of said surfaces.
 6. The lead of claim 1 in which: the membrane hasa tubular configuration.
 7. The lead of claim 6 in which: the membraneis disposed over said outer surface of said housing in an interferencefit.
 8. The lead of claim 6 in which: the membrane is disposed over saidouter surface of said housing in a clearance fit.
 9. The lead of claim 6in which: the membrane is disposed over said outer surface of saidhousing in an even fit.
 10. The lead of claim 1 in which: the insulatinghousing is fabricated of silicone rubber.
 11. The lead of claim 1 inwhich: the membrane comprises a biostable, biocompatible, medical grade,elastic material selected from the group consisting of silicone rubber,polyurethane, polyester, a woven fabric, a knitted fabric, a compositefabric, a memory shaped polymer and a silicone-urethane copolymer. 12.The lead of claim 1 in which: said distal end of the lead body carriesat least two, spaced-apart electrodes comprising a distal electrode anda proximal electrode; said membrane is located between said distal andproximal electrodes; and wherein the lead further includes: a second,thin, flexible membrane surrounding said insulating housing, said secondmembrane being located between the proximal end of the proximalelectrode and the distal end of the connector assembly, the secondmembrane further having an inner surface confronting the outer surfaceof said housing; and a lubricious medium between said inner surface ofsaid second membrane and said outer surface of said housing, saidlubricious medium facilitating movement of said insulating housingrelative to the second membrane in response to frictional engagement ofthe second membrane with adjacent structure.
 13. The lead of claim 12 inwhich: each of said lubricious media comprises a biostable,biocompatible, medical grade material selected from the group consistingof silicone oil, silicone gel, silicone foam, silicone grease, PTFEpowder, mineral oil, mineral paste and mineral powder.
 14. The lead ofclaim 12 in which: each of said lubricious media comprises a lubriciouscoating on at least one of said surfaces.
 15. The lead of claim 1 inwhich: the lubricious medium is a fluid, and the confronting surfacesdefine between them a fluid-tight interface space sealed at oppositeends to contain the fluid.
 16. The lead of claim 1 further comprising: afluid-tight chamber having a first surface defined by the outer surfaceof the insulating chamber and a second surface defined by the innersurface of the membrane.
 17. The lead of claim 16 in which: thelubricious medium is injectable into the fluid-tight chamber.
 18. Thelead of claim 1 in which: membrane deformation comprises wrinkle, twistor wind.
 19. The lead of claim 1 in which: said distal circumferentialseal and said proximal circumferential seal comprise a medical adhesive.